Added test application for reentrant mutexes

* fixed BOARD_INSUFFICIENT_MEMORY for rmutex

tests/rmutex/Makefile

+APPLICATION = rmutex
+include ../Makefile.tests_common
+
+BOARD_INSUFFICIENT_MEMORY := stm32f0discovery weio nucleo-f030 nucleo32-f042
+
+include $(RIOTBASE)/Makefile.include

tests/rmutex/README.md

+Expected result
+===============
+
+When successful, you should see 5 different threads printing their
+PID, priority and recursion depth. The thread with the lowest priority
+should be able to lock (and unlock) the mutex first, followed by the
+other threads in the order of their priority (highest next). If two
+threads have the same priority the lower thread id should acquire the
+lock. The output should look like the following:
+
+```
+main(): This is RIOT! (Version: xxx)
+Recursive Mutex test
+Please refer to the README.md for more information
+
+Recursive Mutex test
+Please refer to the README.md for more information
+
+T3 (prio 6, depth 0): trying to lock rmutex now
+T4 (prio 4, depth 0): trying to lock rmutex now
+T5 (prio 5, depth 0): trying to lock rmutex now
+T6 (prio 2, depth 0): trying to lock rmutex now
+T7 (prio 3, depth 0): trying to lock rmutex now
+main: unlocking recursive mutex
+T6 (prio 2, depth 0): locked rmutex now
+T6 (prio 2, depth 1): trying to lock rmutex now
+T6 (prio 2, depth 1): locked rmutex now
+T6 (prio 2, depth 2): trying to lock rmutex now
+T6 (prio 2, depth 2): locked rmutex now
+T6 (prio 2, depth 3): trying to lock rmutex now
+T6 (prio 2, depth 3): locked rmutex now
+T6 (prio 2, depth 3): unlocked rmutex
+T6 (prio 2, depth 2): unlocked rmutex
+T6 (prio 2, depth 1): unlocked rmutex
+T6 (prio 2, depth 0): unlocked rmutex
+T7 (prio 3, depth 0): locked rmutex now
+T7 (prio 3, depth 1): trying to lock rmutex now
+T7 (prio 3, depth 1): locked rmutex now
+T7 (prio 3, depth 2): trying to lock rmutex now
+T7 (prio 3, depth 2): locked rmutex now
+T7 (prio 3, depth 3): trying to lock rmutex now
+T7 (prio 3, depth 3): locked rmutex now
+T7 (prio 3, depth 4): trying to lock rmutex now
+T7 (prio 3, depth 4): locked rmutex now
+T7 (prio 3, depth 4): unlocked rmutex
+T7 (prio 3, depth 3): unlocked rmutex
+T7 (prio 3, depth 2): unlocked rmutex
+T7 (prio 3, depth 1): unlocked rmutex
+T7 (prio 3, depth 0): unlocked rmutex
+T4 (prio 4, depth 0): locked rmutex now
+T4 (prio 4, depth 1): trying to lock rmutex now
+T4 (prio 4, depth 1): locked rmutex now
+T4 (prio 4, depth 2): trying to lock rmutex now
+T4 (prio 4, depth 2): locked rmutex now
+T4 (prio 4, depth 2): unlocked rmutex
+T4 (prio 4, depth 1): unlocked rmutex
+T4 (prio 4, depth 0): unlocked rmutex
+T5 (prio 5, depth 0): locked rmutex now
+T5 (prio 5, depth 1): trying to lock rmutex now
+T5 (prio 5, depth 1): locked rmutex now
+T5 (prio 5, depth 2): trying to lock rmutex now
+T5 (prio 5, depth 2): locked rmutex now
+T5 (prio 5, depth 2): unlocked rmutex
+T5 (prio 5, depth 1): unlocked rmutex
+T5 (prio 5, depth 0): unlocked rmutex
+T3 (prio 6, depth 0): locked rmutex now
+T3 (prio 6, depth 1): trying to lock rmutex now
+T3 (prio 6, depth 1): locked rmutex now
+T3 (prio 6, depth 2): trying to lock rmutex now
+T3 (prio 6, depth 2): locked rmutex now
+T3 (prio 6, depth 3): trying to lock rmutex now
+T3 (prio 6, depth 3): locked rmutex now
+T3 (prio 6, depth 4): trying to lock rmutex now
+T3 (prio 6, depth 4): locked rmutex now
+T3 (prio 6, depth 4): unlocked rmutex
+T3 (prio 6, depth 3): unlocked rmutex
+T3 (prio 6, depth 2): unlocked rmutex
+T3 (prio 6, depth 1): unlocked rmutex
+T3 (prio 6, depth 0): unlocked rmutex
+
+Test END, check the order of priorities above.
+```
+
+Background
+==========
+This test application stresses a mutex with a number of threads waiting on it.

tests/rmutex/main.c

+/*
+ * Copyright (C) 2016 Theobroma Systems Design & Consulting GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       Test application for testing recursive mutexes
+ *
+ * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ * @author      Martin Elshuber <martin.elshuber@theobroma-systems.com>
+ * @}
+ */
+
+#include <stdio.h>
+
+#include "rmutex.h"
+#include "thread.h"
+
+#define THREAD_NUMOF            (5U)
+
+extern volatile thread_t *sched_active_thread;
+
+static char stacks[THREAD_NUMOF][THREAD_STACKSIZE_MAIN];
+
+static const char prios[THREAD_NUMOF] = {THREAD_PRIORITY_MAIN - 1, 4, 5, 2, 4};
+static const char depth[THREAD_NUMOF] = {5, 3, 3, 4, 5};
+
+static rmutex_t testlock;
+
+static void lock_recursive(char n, char depth)
+{
+    volatile thread_t *t = sched_active_thread;
+
+    printf("T%i (prio %i, depth %i): trying to lock rmutex now\n",
+        (int)t->pid, (int)t->priority, (int)n);
+    rmutex_lock(&testlock);
+
+    printf("T%i (prio %i, depth %i): locked rmutex now\n",
+           (int)t->pid, (int)t->priority, (int)n);
+
+    if (n + 1 < depth)
+        lock_recursive(n + 1, depth);
+
+    thread_yield();
+
+    rmutex_unlock(&testlock);
+
+    printf("T%i (prio %i, depth %i): unlocked rmutex\n",
+           (int)t->pid, (int)t->priority, (int)n);
+}
+
+static void *lockme(void *arg)
+{
+    intptr_t depth = (intptr_t)arg;
+
+    lock_recursive(0, depth);
+
+    return NULL;
+}
+
+int main(void)
+{
+    puts("Recursive Mutex test");
+    puts("Please refer to the README.md for more information\n");
+
+    rmutex_init(&testlock);
+
+    /* lock mutex, so that spawned threads have to wait */
+    rmutex_lock(&testlock);
+    /* create threads */
+    for (unsigned i = 0; i < THREAD_NUMOF; i++) {
+        thread_create(stacks[i], sizeof(stacks[i]), prios[i], 0,
+                    lockme, (void*)(intptr_t)depth[i], "t");
+    }
+    /* allow threads to lock the mutex */
+    printf("main: unlocking recursive mutex\n");
+
+    rmutex_unlock(&testlock);
+
+    rmutex_lock(&testlock);
+    puts("\nTest END, check the order of priorities above.");
+
+    return 0;
+}

tests/rmutex/tests/01-run.py

+#!/usr/bin/env python3
+
+# Copyright (C) 2016 Theobroma Systems Design & Consulting GmbH
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
+# Author: Martin Elshuber <martin.elshuber@theobroma-systems.com>
+
+import os
+import sys
+
+sys.path.append(os.path.join(os.environ['RIOTBASE'], 'dist/tools/testrunner'))
+import testrunner
+
+thread_prio = {
+        3:  6,
+        4:  4,
+        5:  5,
+        6:  2,
+        7:  4
+        }
+
+lock_depth = {
+        3:  5,
+        4:  3,
+        5:  3,
+        6:  4,
+        7:  5
+        }
+
+def thread_prio_sort(x):
+    return thread_prio.get(x)*1000 + x
+
+def testfunc(child):
+    for k in thread_prio.keys():
+        child.expect(u"T%i \(prio %i, depth 0\): trying to lock rmutex now" %
+                     (k, thread_prio[k]))
+
+    pri_sorted = sorted(thread_prio, key=thread_prio_sort);
+    for T in pri_sorted:
+        for depth in range(lock_depth[T]):
+            child.expect(u"T%i \(prio %i, depth %i\): locked rmutex now" %
+                         (T, thread_prio[T], depth))
+
+if __name__ == "__main__":
+    sys.exit(testrunner.run(testfunc))